At first, the relevance of the title seems obvious. The Trial refers to the main character's trial, right? But when you read the novel, you may notice that…there's no actual trial in the book. There's an inquiry in Chapter 2, but the trial itself – with opening statements, defense, prosecution, testimony, and verdict – never actually happens.
No, you didn't misread the book. Part of the trouble is that, since we're reading the book in its English translation, the title doesn't seem to fit. The original German title – Der Prozeß – does mean "trial," but it also refers to all the stuff surrounding the trial, including the inquiry in Chapter 2, criminal investigations, and all of the legal work that goes into a trial, such as Huld's petition. Either way, both the English and the German titles stress K.'s experience of his trial as one of seemingly interminable bureaucratic maneuvers.